In many industrial machines, such as packaging and textile machines or sheet-fed offset printing machines, a plurality of movements have to be carried out regularly as a function of a central guide movement. The guide movement, which is carried out by a guide axis, is as a rule a cyclically repeated movement, for example the rotation of an axis. One general requirement for the guide movement is that lower-order movements which are carried out by the slave axes or follower axes follow the guide movement as exactly as possible in accordance with their predefinitions.
Classically, these are carried out by means of a mechanical construction, for example by means of cam disks, as they are known, or by a cam control system. In recent times, electronically regulated drives have been used both for the guide axis and for the slave axes, and dispensing with the positive mechanical coupling. One may speak of this as an electronic transmission. The measurement of the guide axis movements is in this case mostly carried out by means of a rotary encoder. The desired angles for the regulation of the slave axes are determined as a function of the measured guide axis angles.
The illustration according to FIG. 2 shows a block diagram for generating the slave axis setpoints in the conventional manner outlined. An electrically driven guide axis L_A changes its position by assuming various position angles φL, which are registered by a rotary encoder WG. This supplies position measured values φL—meas, with which a function block F is driven which describes the geometric relationship between the movements φL—meas of the guide axis L_A and the desired movements φS—sp of the follower axis or slave axis S_A. This can be carried out in the form of a mathematical function φS—sp=f(φL—meas) or else, for example, by means of a table, in which pairs of values are deposited which represent corresponding locational positions between the guide axis and the slave axis. Using the position setpoints φS—sp generated by the function block F on the output side, the slave axis S_A is finally driven.
Using electronic drives as described above and shown in FIG. 2, the actual angles φS—act of the slave axes always lag behind their setpoints φS—sp, since each position control system is afflicted with a specific delay. The difference between the position setpoint φS—sp and the position measured value φS—act is referred to as the lag error. If, for example, a bus system is used for the transmission of the measured guide axis measured values to the slave axes, then the lag error increases again because of the transport time on the bus. The latter is also true for those slave axes which are not regulated but merely controlled.